The mayor of the small Texas city north of Waco devastated by an explosion at a fertilizer plant said that 35 to 40 people were unaccounted for.

West, Texas, Mayor Tommy Muska gave that estimate to ABC News as search and rescue teams continued to look for survivors and missing people amid flattened and devastated buildings near the scene of Wednesday evening's explosion.

Volunteer firefighters battling a blaze at the plant that preceded the blast were among the missing.

The fire and explosion just before 8 p.m. Wednesday at the West Fertilizer Plant in West, Texas, prompted widespread evacuations and sent more than 160 injured people to hospitals.

Authorities this morning said they feared five to 15 people could be dead, but later said those figures were just an estimate.

"We have confirmed fatalities at this time. We don't have the exact amount," Texas Department of Public Safety Sgt. Jason Reyes said at a news conference this afternoon.

However, Dallas Fire-Rescue Captain Kenny Harris who was initially reported missing, was identified this evening as killed in the blast, according to a news release from the city of Dallas.

Harris was off duty at the time of the explosion and was not a volunteer firefighter, but responded as a helper. He was not believed to have been involved in any firefighting activity, according to the statement.

"Capt. Harris' response is typical of all our first responders; night and day, no matter where they are, no matter if they are on or off duty they respond with the greatest acts of bravery," Dallas City Manager Mary Suhm said in a statement. "The city of Dallas and the citizens of Dallas have lost a real role model."

The explosion devastated the area that officials described as a highly-populated neighborhood.

"It ranges from broken windows to complete devastation," Waco Police Department Sgt. William Swanton said at a news conference today. "There are homes that are no longer homes."

At some buildings, "walls were ripped off, roofs were peeled back," the sergeant said.

"The apartment complex [near the plant] looks like it was a bombing site of an explosion -- the kind that you seen in Baghdad," Texas Attorney General Greg Abbot told reporters this evening. "It was utterly destroyed."

State Trooper D.L. Wilson of the Texas Department of Public Safety described the initial fertilizer plant blast as "massive -- just like Iraq, just like the Murray Building in Oklahoma City. The same kind of hydrous [ammonia] exploded, so you can imagine what kind of damage we're looking at."

Swanton said authorities were still in search-and-rescue mode and are not yet in recovery mode.

"The town is secure. There are plenty of law enforcement officials that are stationed around the town," Swanton said. "There is no fire out of control. There is no chemical escape from the fertilizer plant that is out of control."

However, as they prepared to investigate the explosion site, officials said they were treating it as a crime scene.

"We are not indicating that it is a crime, but we don't know," Swanton said. "What that means to us is that until we know that it is an industrial accident, we will work it as a crime scene. ATF [the federal Bureau of Alcohol, Tobacco, Firearms and Explosives] is conducting the main investigation."

The Red Cross, mental health agencies and grief counselors were on hand to help the community, in addition to the neighbors who were already assisting each other.

"That is a very tight-knit, very family packed, family-oriented community," Swanton said of the town of about 2,800 people. "They are leaning on each others' shoulders."

This evening, the singer Willie Nelson, who grew up nearby, released a statement that testified to the nature of the region.

"West is just a few miles from my hometown of Abbott," Nelson said. "I was born and raised here and it was my backyard growing up. This is my community. These friends and neighbors have always been and are still a part of my life. My heart is praying for the community that we call home."

President Obama, in a statement, extended his condolences to the people of West and thanked first responders.

"A tight-knit community has been shaken, and good, hard-working people have lost their lives," he wrote.

"My administration, through FEMA and other agencies, is in close contact with our state and local partners on the ground to make sure there are no unmet needs as search and rescue and response operations continue."

Texas Gov. Rick Perry said he has requested an emergency declaration from the president for West.

"Last night was truly a nightmare scenario for that community," Perry said at a news conference today. "Anyone who grew up ... in a small town like West, they know that this tragedy has most likely hit every family, has touched practically everyone in that town."

The disaster even drew condolences from Pope Francis, who tweeted, "Please join me in praying for the victims of the explosion in Texas and their families."

Earlier concerns about the possibility of dangerous ammonia fumes and shifting winds subsided by morning as fires died down, Swanton said before 6 a.m. ET.

So, too, did fears of looting. Though authorities expressed concerns about it earlier today, they later said a case initially reported to them was an isolated incident.

"I have confirmed at least there was an incident last night when they thought they may have had a looter," Swanton said, adding that the incident occurred "very, very early in the scenario."

He said there was no arrest and the problem is "not rampant," but people are still being kept out of the main disaster area.

Witnesses reported heavy fire or concussive damage to a middle school, homes and the apartment complex near the plant, as well as to a nursing home, where more than 130 residents were evacuated, Mayor Muska said.

Buildings in a radius of about five blocks around the plant -- including at least 60 more homes -- were heavily damaged by the blast, officials said.

"It was almost tornadic in effect," Swanton said. "It looked like to me one home would be fine and next to it there would be extreme devastation."

It was felt 20 to 30 miles away, witnesses said, and near the plant it burned buildings, knocked down people, blew out windows and, according to Wilson, left the damaged apartment complex looking like "just a skeleton standing up."

"It's total chaos," West City Councilwoman Cheryl Marak said soon after the blast, according to ABC News Radio. "There's ambulances and fire trucks and police cars from everywhere."

Marak told ABC News that the explosion killed her pet dog and destroyed her house about 2 1/2 blocks from the plant, as well as houses around it.

"With the explosions, the whole street lifted up," she told ABC News. "It was like a massive bomb went off. It demolished both my houses, my mother's and mine."

"I think everything around us is pretty much just gone," she added, according to ABC News Radio.

Keith Williams, a local resident, said his house also was destroyed.

"All the ceilings are out," Williams said, according to ABC News Radio. "The windows are out. The brick's knocked off the house. My big garage out back is half blowed in."

He also saw "people with all their houses tore up across the street from me, on each side of me."

The fertilizer plant exploded around 7:50 p.m. local time Wednesday, according to the Texas Department of Public Safety.

Emergency response audio told the story of the chaos among firefighters and others at the scene.

"We need every ambulance we can get this way," one snippet said. "A bomb just went off. It's pretty bad."

"Firefighters down," another said. "There has been an explosion."

"The rest home has been seriously damaged. We have many people down. Please respond."

There were subsequent explosions around 10 p.m., ABC News affiliate WFAA reported. The cause of the explosions was unconfirmed, but a dispatcher was heard warning crews to move away from chemicals in unexploded tanks.

The fertilizer plant was fined $2,300 by the Environmental Protection Agency in 2006 for failing to have a risk management plan that met federal standards, the EPA told ABCNews.com in an email.

The plant was not penalized by the EPA again after that incident and has not had any major accidents in the last five years.

Another EPA report showed that West Fertilizer Co. reported the "worst possible scenario ... would be a 10-minute release of ammonia gas that would kill or injure no one," according to the Dallas Morning News.